On the issue of the scientist with terrorist connections:
The goal may not have been to extract information to use as a WMD. More likely in my mind, he may have been there to see if he could destroy CERN with carefully placed explosives (or paper clips). Destroying CERN would be quite the coupe. 10 years ago terrorists changed the existing hijacking paradygm to catastrophic effect.
On the issue of where the aliens are:
Upthread someone gave a timeline of a colinized planet sending out another colony ship in 500 years. This is unrealistic.
First, a colony ship must be huge and self-sufficient. We're not talking a small apollo type ship to make a dash, we're talking a Rama type ship. One ship would be a tremendous drain on a world economy.
So a civilization makes a colony ship and off they go to the nearest life supporting planet. Bear in mind their colony ship is self-supporting, so they are in no rush. When they get "there", they spend a few years studying the planet before they commit. When they commit, they would have no need to send out another colony ship until they've maxed out the use of the new planet, which, based on the only example we have would take not 500 years, but more like 5,000 - 10,000 years. Since they've learned how to build self-sustaining colony ships, they've also learned how to live in a self-sustaining manner, so it may take much longer to "use up" a planet. Also, these colony ships have no need to travel anywhere near the speed of light, they can meander along at any speed they choose.
Space flight is dangerous, and compared to the forces of the universe, any space colony ship would be fragile. While the colony ship is traveling to a new localle, they are at risk, one oops and they're done. Also, once they commit to colonizing a planet, they again have all their eggs in one fragile basket.
What do they do when they encounter another space faring intellegence? War is a definate possibility, and that takes a lot of resources, and at interstellar distances could take extremely long. Even without war, peace and integration take a long time. Or they may just decide not to deal with that group and just expand in a different direction.
Deciding to colonize another planet is expensive and arduous and would only be undertaken as a last resort. Colonizing for it's own sake doesn't help the original world, in fact the original world losing major resources, forever.
We also assume that other space faring species would naturally want to go forth and colonize. They may simply not have the urge. Also, look around... we're using up our resources and still have no real space faring ability. It may be that by time we realize to survive we must send out a colony ship, we may still not have the ability, or may have used up the resources to the extent that it's not possible to both build a colony ship and support current society. This situation may end up being a truism of a planets lifecycle.
There is also a lot of intellegence that may never have the biological tools to become space faring. Look at dolphins, they may have or may get intellegence equal to ours, but no biological tools to do anything but think great thoughts and have great discussions while swimming around their vast oceons on their little blue planet.
But, because the aliens aren't here, I think we can conclude a few things: 1) FTL travel is not possible; 2) Time Travel is not possible; 3) Space is big and dangerous.